This invention relates to an apparatus and a method for fabricating microminiature devices and, more particularly, to a multiple-beam scanning technique for use in a charged-particle-beam exposure system.
U.S. Pat. No. 3,900,737, which issued to R. J. Collier and D. R. Herriott on Aug. 19, 1975, describes an electron beam exposure system (EBES) that is a practical tool for generating high-quality fine-featured integrated circuit masks. The system is also capable of exposing patterns directly on resist-coated semiconductor wafers. EBES combines continuous translation of the mask or wafer substrate with periodic deflection of the electron beam in a raster-scan mode of operation.
An advantageous modification of EBES is described in a commonly assigned copending application of R. J. Collier and M. G. R. Thomson, Ser. No. 655,427, filed Feb. 5, 1976, now abandoned and replaced by a continuation filed Nov. 29, 1977, Ser. No. 855,608. In this modified system, the pattern-writing speed of EBES is increased by utilizing a new mode of raster scanning. In the new mode, the writing spot dimensions of the scanning electron beam are varied in a high-speed way during the raster scanning process.
Efforts have been directed at trying to devise still other ways of increasing the pattern-writing speed of EBES. The primary motivation for these efforts is the desire to increase the throughput of such a system. In that way the cost per unit area exposed by the scanning electron beam is reduced and the economic attractiveness of EBES as a lithographic tool is enhanced. Also, another motivation for devising such modifications is the realization that in such a faster system higher throughput can be traded for a finer address structure or for the use of a less sensitive electron resist.
Moreover, in the course of trying to develop improved EBES machines it has been recognized that so-called proximity effects cause undesirable variations in the electron dose delivered to different address positions of the resist material. Hence, efforts have also been directed at attempting to devise simple and reliable techniques for compensating for such effects.